JPH0631147A - Production of ultrafilter membrane - Google Patents

Abstract

PURPOSE:To obtain the ultrafilter membrane made of plate-like or hollow fiber ultrafilter membrane which has membrane strength durable for practical use and high flow rate while maintaining fractional property. CONSTITUTION:The film-forming stock soln. dissolving -SO3Na type sulfonated polysulfone is extended on a substrate, immersed into an aq. coagulating bath containing inorg. acid and inorg. sodium salt, gelatificated and a plate-like ultrafilter membrane is obtained, and the spinning stock soln. dissolving -SO3Na type sulfonated polysulfone is extruded with the aq. core liq. containing inorg. acid and inorg. sodium salt from a double annular nozzle, immersed into a water coagulating bath or the same aq. coagulating bath as the core liq., gelatificated and the hollow fiber ultrafilter membrane is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an ultrafiltration membrane. More specifically, it relates to a method for producing a flat membrane-shaped or hollow fiber-shaped ultrafiltration membrane made of sulfonated polysulfone.

[0002]

2. Description of the Related Art In recent years, in order to search for the possibility of a new separation mechanism, research has been conducted on a membrane having an ultrafiltration membrane to which a charging effect is added. Above all, many studies have been made on sulfonated polysulfones. Among the sulfonation polysulfone film forming methods, the dry method in which the sulfonation polysulfone film forming solution is cast on the substrate and the solvent is evaporated to form a flat film-like film, the active layer becomes dense and reverse osmosis occurs. It is suitable for producing high level membranes, but ultrafiltration level membranes have not been obtained.
Further, as compared with the wet method, precise control is required during film formation.

There is also a method in which the sulfone group of sulfonated polysulfone is made into -SO ₃ H type, and this is made into an alcohol solvent solution, and then coated on a polysulfone microporous membrane, but in this case, an extra coating is required. Not only is it troublesome, but there is also the problem that a strong active layer film cannot be obtained.

On the other hand, in the method in which the sulfone group of sulfonated polysulfone is made -SO ₃ Na type, and this is dissolved in a solvent and then immersed in water which is a coagulation bath, the charged members of this resin repel each other. However, it is impossible to obtain a film that can be used practically. In order to suppress such repulsion, it has been experimentally performed to add an inorganic acid such as hydrochloric acid as an electrolyte to the coagulation bath, but the performance of the film produced by such a method is
It is inferior to commercially available polysulfone ultrafiltration membranes in terms of flow characteristics.

Further, an ultrafiltration membrane composed of sulfonated polysulfone or a mixture thereof with polysulfone has been previously proposed by the present applicants (Japanese Patent Laid-Open No. 61-249504).
No. 62-45303, No. 62-49908, No. 63-1
37703 gazette), since water is used in the coagulation bath in these proposed membrane forming methods, the ion exchange capacity of the sulfonated polysulfone must be reduced in order to obtain a certain degree of membrane strength. However, since the characteristic of the sulfonated polysulfone membrane is the point of charge, there was a problem that it was difficult to obtain a strong membrane in a water coagulation bath when the amount of charge was increased.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to produce a sulfonated polysulfone ultrafiltration membrane in the form of a flat membrane or a hollow fiber, which has a membrane strength that can withstand practical use and which maintains a fractionation characteristic and has a high flow rate. An object is to provide a method for manufacturing a hypermembrane.

[0007]

The object of the present invention is as follows.
This is achieved by the following two methods. (1) -SO ₃ Na-type sulfonated polysulfone was dissolved in a film-forming stock solution on a substrate, followed by immersion in an aqueous coagulation bath containing an inorganic acid and an inorganic sodium salt to cause gelation,
Method for producing flat membrane ultrafiltration membrane by wet method (2) -SO ₃ Na-type sulfonated polysulfone is dissolved in a spinning stock solution with an aqueous core solution containing an inorganic acid and an inorganic sodium salt to form a double layer. A method for producing a hollow fiber ultrafiltration membrane by a dry-wet method or a wet method by extruding from an annular nozzle, immersing it in a water coagulation bath or in the same aqueous coagulation bath as the core liquid, and causing it to gel

-SO ₃ Na type sulfonated polysulfone is available from Jour.
nal of Applied Polymer Science Vol. 20, p. 1885 (1976)
It can be obtained according to the method described in. The number of sulfone groups per repeating unit of the polysulfone resin can be changed by changing the addition ratio of the sulfonating agent, and can be confirmed by the ion exchange capacity of the obtained resin. In order to obtain a strong membrane, one having an ion exchange capacity of about 2 meq / g or less, preferably about 05 to 1.5 meq / g is generally used.

The membrane-forming stock solution or spinning stock solution is prepared by adding -SO ₃ Na type sulfonated polysulfone to a concentration of about 10 to 30% by weight in a water-soluble organic solvent such as N-methyl-2-pyrrolidone, dimethylacetamide or dimethylformamide. Prepared as a dissolved solution. In these stock solutions, in order to control the pore size of the active layer (skin layer) of the ultrafiltration membrane to be formed, an inorganic lithium salt that is completely dissolved in this stock solution, such as lithium chloride, lithium nitrate, etc. It is preferable to add about 1 to 5% by weight.

The film-forming into a flat film by the wet method using such a film-forming stock solution is carried out by casting the film-forming stock solution on various substrates,
It is performed according to the usual method of immersing in an aqueous coagulation bath and gelling. At this time, an aqueous solution containing an inorganic acid and an inorganic sodium salt is used as the aqueous coagulation bath.

As described above, when water is used in the coagulation bath, the charge amount of the resin is large, so that the charge repels each other and gelation does not occur, or only a very brittle film is obtained. For this purpose, an inorganic acid such as hydrochloric acid or nitric acid is added as an electrolyte. These electrolytes
It is also necessary as a hydrogen cation for forming a film while replacing Na of the —SO ₃ Na group with H.

In this case, the molecular weight cutoff of the membrane can be changed by changing the concentration of the inorganic acid. That is,
When the concentration of the inorganic acid is increased, the molecular weight cutoff of the membrane shifts to the larger one, and the amount of water permeation increases. However, the water permeability is at a low level of about 1/2 to 1/5 as compared with a commercially available polysulfone ultrafiltration membrane having similar fractionation characteristics.

Therefore, in order to improve the water permeability while maintaining such fractionation characteristics, the addition of an inorganic sodium salt such as sodium chloride, sodium nitrate or sodium sulfate, preferably sodium chloride, as the second electrolyte. It has been found to be effective. These second electrolytes are substances that increase the ionic strength without changing the hydrogen cation strength. These two types of electrolytes have an inorganic acid content of about 20 to about 1000 ml per 1000 ml of the aqueous coagulation bath when concentrated hydrochloric acid is used.
500 ml and inorganic sodium salts are generally used in proportions of about 15 to 200 g.

The hollow fiber membrane is formed by a dry-wet method or a wet method using the same spinning solution as the film-forming stock solution, using a double annular nozzle according to a usual method. At this time, an aqueous solution containing an inorganic acid and an inorganic sodium salt is used as the core liquid, and not only the same aqueous coagulation bath as the core liquid but also a water coagulation bath can be used as the coagulation bath.

[0015]

According to the method of the present invention, by using a coagulation bath containing two kinds of electrolyte substances, a flat membrane having a membrane strength that can withstand practical use and having a high permeation water amount while maintaining the fractionation characteristics is obtained. Alternatively, a hollow fiber sulfonated polysulfone ultrafiltration membrane can be obtained.

[0016]

EXAMPLES The present invention will now be described with reference to examples.

Example 1-SO ₃ Na type sulfonated polysulfone (ion exchange capacity 1.5 meq / g) 20 parts by weight, 3 parts by weight of lithium chloride and 77 parts by weight of N-methyl-2-pyrrolidone were used as a membrane forming solution. , Cast on a glass plate and immediately use 42 ml of concentrated hydrochloric acid and sodium chloride.
The film was immersed in 1000 ml of an aqueous coagulation bath containing 29.3 g and gelled to obtain a flat film.

Example 2 In Example 1, the amount of sodium chloride was changed to 58.6 g.

Comparative Example 1 When a coagulation bath containing only water was used in Example 1, the obtained film was brittle and could not be put to practical use.

Comparative Example 2 In Example 1, an aqueous coagulation bath containing no sodium chloride was used.

With respect to the flat membranes obtained in Examples 1 and 2 and Comparative Example 2, the rejection rate of polyethylene glycol (PEG) having an average molecular weight of 20,000 and the amount of permeated water were measured.
The following results were obtained. Example PEG blocking rate (%) Permeate flow rate ( ml / hr · kg / cm ² · cm ² ) Example 1 92.0 57 〃 2 91.3 73 Comparative Example 2 90.7 17

Example 3 In Example 1, the film-forming stock solution was used as the spinning stock solution, and the same composition as the aqueous coagulation bath was used as the core solution, which was dry-wet spun from the double annular nozzle, and only water 20 cm away from the nozzle outlet was used. Was immersed in the coagulation bath of the above and gelled.

Comparative Example 3 In Comparative Example 2, the film-forming stock solution was used as the spinning stock solution, and the same composition as the aqueous coagulation bath containing no sodium chloride was used as the core solution, which was subjected to dry-wet spinning from the double annular nozzle, and from the nozzle outlet. It was dipped in a coagulation bath containing only 20 cm of water and gelled.

With respect to the hollow fiber membranes obtained in Example 3 and Comparative Example 3, the PEG inhibition rate and the amount of permeated water were measured.
The following results were obtained. Example PEG blocking rate (%) Permeate flow rate ( ml / hr · kg / cm ² · cm ² ) Example 3 85.2 35 Comparative Example 3 80.3 15

Claims (4)

[Claims] 1. A method for casting a film-forming stock solution in which -SO ₃ Na type sulfonated polysulfone is dissolved on a substrate, and then immersing it in an aqueous coagulation bath containing an inorganic acid and an inorganic sodium salt to cause gelation. A method for producing a flat membrane ultrafiltration membrane by a wet method, which is characterized by: 2. The method for producing a flat membrane ultrafiltration membrane according to claim 1, wherein a membrane-forming stock solution in which an inorganic lithium salt is further dissolved is used. 3. A spinning stock solution in which -SO ₃ Na type sulfonated polysulfone is dissolved is extruded from a double annular nozzle together with an aqueous core solution containing an inorganic acid and an inorganic sodium salt, and the same as in the water coagulation bath or the core solution. A method for producing a hollow fiber ultrafiltration membrane by a dry-wet method or a wet method, which comprises immersing in an aqueous coagulation bath to cause gelation. 4. The method for producing a hollow fiber ultrafiltration membrane according to claim 3, wherein a spinning stock solution in which an inorganic lithium salt is dissolved is used.